1. Field of the Invention
The present invention relates to an optical disk device for learning disturbance of an optical disk. More particularly, the present invention relates to an optical disk device and a disturbance learning method for the optical disk device for carrying out reliable disturbance learning by reducing a servo gain during learning.
2. Description of the Related Art
Recently, an optical disk device such as DVD (Digital versatile Disc) has been developed and widely known. In such an optical disk device or the like, it is required to improve operational reliability more remarkably.
As one example of such an optical disk device, in Jpn. Pat. Appln. KOKAI Publication Nos. 8-77589 and 9-50303, there is disclosed an optical disk device having a stable control system for taking a correlation between an error signal before one cycle and a current error signal, and increasing a gain of the control system when this correlation is strong, or reducing the gain of the control system when the correlation is weak so as not to respond to a component other than damage or dust and cyclic disturbance such as external vibration.
Similarly, in Jpn. Pat. Appln. KOKAI Publication No. 11-86309, there is disclosed a learning compensator comprising a signal generator circuit which changes along with the rotation number, the learning compensator generating a timing for learning, thereby enabling learning in which a time delay becomes constant even if the rotation number changes, in an optical disk device having a changed rotation number.
In the prior art disclosed in these references, respectively, a repetition learning device is used to lean a disturbance component generated along with the disk rotation to compensate for the component in a feed forward manner.
However, in these disturbance learning processes, there is a problem that a disturbance value is small as compared with a control gain, thus disabling sufficient learning.
In addition, in the case of an optical disk device having a changed rotation number, since a disturbance suppression rate changes depending on a frequency and a positioning error quantity changes depending on the frequency, there is a problem that a precise disturbance value cannot be obtained.
Further, in a recording type optical disk device, since a disk reflection index differs depending on whether or not information is recorded in a target optical disk, that is depending on a recorded region or an unrecorded region, it is inevitable that the gain of the control system changes frequently. Therefore, a precise disturbance value cannot be obtained in the recording type optical disk.
In other words, in the conventional optical disk device, since a value of disturbance information in an optical disk is comparatively small, the disturbance value is affected by the gain of servo control or a change in the rotation number of the optical disk. In addition, in the case of the recording type optical disk, the disturbance value is affected by a difference between reflection indexes of the recorded region and the unrecorded region. Thus, there is a problem that a process of learning of precise disturbance information cannot be carried out.